Preheat your oven to 350 ℉ or 175 ℃. Prepare two baking sheets by lining them with parchment paper.
In a large bowl with a hand mixer or in the bowl of your stand mixer, cream the butter and sugar together on medium-high speed until the mixture is creamy and smooth (for several minutes).
Add the peanut butter and mix well on medium speed until well combined, scraping down the sides of the bowl to make sure it's all incorporated.
Add the egg and vanilla and mix well. Scrape down the sides of the bowl.
Add the flour, baking soda and salt and mix on low speed until combined and there are no more streaks of flour.
Using a cookie scoop or a tablespoon, portion the cookie dough and roll into 24 balls. Roll each ball in the granulated sugar and place them on the baking sheets spaced apart.
Bake for 8-10 minutes or until the cookies are crackly on top and the centres are soft but set.
Cool on the pans for about 2 minutes before pressing a milk chocolate candy into the top of each of the warm cookies. It's critical to do this while the cookies are very warm.
Let the cookies cool on their pans for 20 minutes before moving them to a cooling rack to cool completely,